Although previous studies have suggested that nociceptive afferents from intra-oral and facial structures are organized differently in the trigeminal sensory nucleus (TSN), more detailed data are needed. The present study aimed to fill this gap, by examining the changes in the expression of c-Fos within the rat TSN following high- and low-intensity electrical stimulation applied to the Gasserian ganglion (GG). A low-intensity stimulus (0.1 mA) induced c-Fos in many neurons in the dorsomedial subdivision (Vodm) of the oral subnucleus (Vo; mean +/- SEM in a certain segment = 163.0 +/- 42.7), in the medial part of the dorsomedial subdivision (Vidm) of the interpolar subnucleus (Vi; 120.5 +/- 40.1), in the medial corner of the magnocellular zone (VcIII/IV; 47.5 +/- 10.5), and in the superficial layers (VcI/II; 1330.0 +/- 65.6) along the entire length of the dorsomedial-ventrolateral axis of the caudal subnucleus (Vc). A modest number of Fos-positive neurons were induced in the dorsal principal subnucleus (Vp; 10.0 +/- 4.9) and in the lateral VcIII/IV (11.5 +/- 1.6). A high-intensity stimulus (1.0 mA) significantly increased the number of Fos-positive neurons in each subdivision compared with the low-intensity stimulus (Vp 32.3 +/- 10.8; Vodm 270.3 +/- 75.3; Vidm 189.3 +/- 38.5; medial VcIII/IV 77.5 +/- 18.2; lateral VcIII/IV 24.8 +/- 9.3; VcI/II, 2155.8 +/- 470.2). At both low- and high-intensity stimulation, the fields where Fos-positive neurons appeared are restricted to the dorsal or dorsomedial subdivisions of the rostral subnuclei, Vp, Vo and Vi, where the main projectional fields of primary afferents from the intraoral structures are found, while Fos-positive neurons were distributed in the entire VcI/II, along the dorsomedial-ventrolateral axis of Vc, where the main projectional fields of primary afferents from the facial skin are found. The threshold to induce c-Fos is, however, different according to the fields. These results suggest that nociceptive processing in the intra-oral region is mediated through the entire length of the rostro-caudal axis of TSN, but is mediated primarily through VcI/II in the facial region.

This study characterizes the developmental expression of NADPH-diaphorase from embryo to adulthood in the forebrain, midbrain and cerebellum of rat brain via histochemical staining. On embryonic day 12 no neurons stained. Labeling was observed in certain nuclei from E15 through the postnatal period to adulthood. Labeling in neurons increased or maintained a constant level with increased age. The embryo demonstrated substantial labeling in neurons of the caudate putamen, bed nucleus of the stria terminalis, preoptic area, lateral hypothalamic area, paraventricular thalamic nucleus, ventromedial hypothalamic nucleus, magnocellular nucleus posterior commissure, and periaqueductal central gray. Additional neuronal labeling was observed postnatally in the olfactory bulb, cerebral cortex, amygdala, various nuclei of the thalamus, interpeduncular nucleus, linear nucleus of the raphe, pretectal area and superior colliculus. In the cerebellum, labeling appeared only after P14 in cells of the molecular cell layer and granular cell layer. The sizes of labeled neurons developed significantly from P4 to P14 in several nuclei. The distinctive temporal and spatial expression pattern of NADPH-diaphorase implies that the NO/cGMP system may play an important role in physiological and developmental functions.

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We examined the effects of systemic administration of a GABA(A) receptor agonist, muscimol, or antagonist, bicuculline, on the expression of c-Fos protein induced 3h after electrical stimulation of the trigeminal ganglion at low (0.1 mA) or high intensities (1. 0 mA) in the urethane-anesthetized rat. In saline-treated rats, 10 min stimulation of the trigeminal ganglion induced c-Fos-immunopositive neurons throughout the full extent of the ipsilateral superficial layers of the trigeminal nucleus caudalis, and dorsal or dorsomedial part of the nuclei rostral to obex (trigeminal nucleus principalis, dorsomedial nucleus of trigeminal nucleus oralis, dorsomedial nucleus of trigeminal nucleus interpolaris). Animals stimulated at 1. 0 mA induced a significantly higher number of labeled neurons in all trigeminal sensory nucleus than animals stimulated at 0.1 mA. In rats treated with 1mg/kg i.p. muscimol and stimulated at 0.1 mA, the numbers of Fos-positive neurons in trigeminal nucleus caudalis, dorsomedial nucleus of trigeminal nucleus interpolaris, and dorsomedial nucleus of trigeminal nucleus oralis were significantly decreased. However, after stimulation at 1.0 mA, the numbers of Fos-positive neurons in the superficial layers of trigeminal nucleus caudalis was increased and no changes occurred in the numbers of Fos-positive neurons in the magnocellular zone of trigeminal nucleus caudalis, the dorsomedial nucleus of trigeminal nucleus interpolaris, or dorsomedial nucleus of trigeminal nucleus oralis compared to saline-treated controls. In rats treated with 2mg/kg i.p. bicuculline and stimulated at 0.1 mA, the number of Fos-positive neurons increased in the superficial layers of trigeminal nucleus caudalis and trigeminal nucleus principalis. However, after stimulation at 1.0 mA, the number of Fos-positive neurons was unchanged in superficial layers of trigeminal nucleus caudalis, but decreased in the magnocellular zone of trigeminal nucleus caudalis, dorsomedial nucleus of trigeminal nucleus interpolaris and dorsomedial nucleus of trigeminal nucleus oralis. There was a specific loss of Fos-positive neurons in the maxillary and ophthalmic divisions (ventrolateral half) of trigeminal nucleus caudalis. These results indicate that the expression of c-Fos in the trigeminal nucleus is differentially regulated through GABA(A) receptors in a manner that is dependent on the nucleus and the type of primary afferents that are activated by different stimulus intensities.